In U.S. Pat. No. 4,071,335 there is described a gettering alloy consisting of the intermetallic compound Zr.sub.2 Ni and its use in nuclear reactor fuel elements for the sorption of water and water vapour.
In UK specification No. 1,370,208 there is described, for the same use, a ternary gettering alloy Zr--Ti--Ni able to stoichiometrically sorb water and water vapour without the release of hydrogen.
It is known that nuclear reactor fuel elements normally comprise an outer sheath of a material based on zirconium, within which there are pellets of fuel material, such as UO.sub.2. During use of the fuel element within the reactor there is release of water, normally in the form of water vapour, and this water vapour reacts with the components of the tubular sheath material, with the undesirable consequence of a liberation of hydrogen. The reaction between hydrogen and the zirconium of the tubular sheath material of the fuel elements leads to embrittlement and then fracture of the sheath material.
Getter materials used up to the present moment in this field must work at temperatures of at least 350.degree. C. to ensure that during sorption of water and water vapour no hydrogen is liberated. This temperature corresponds to that at which the getter material functions during normal nuclear reactor working. However, during start-up of the reactor and when it works at low out-put, the temperature may be considerably lower. In these conditions, with known getters there is the danger of hydrogen release.